The present invention relates to a storage system and an operation method of a storage system.
For instance, government agencies, companies, educational institutions and others manage data with a relative large storage system for handling various data in large quantities. This storage system, for example, is configured by including a storage device such as a disk array device. For instance, a storage device is configured by disposing a plurality of memory apparatuses in an array to provide a memory area based on RAID (Redundant Array of Inexpensive Disks). At least one or more logical volumes are formed on a physical memory area provided by the memory apparatus group, and this logical volume is provided to a host computer (hereinafter abbreviated as “host”). By transmitting a write command or read command, the host is able to write and read data into and from the logical volume.
Data to be managed by companies and others is increasing daily. Thus, companies and others, for example, equip the storage system with a new storage device to expand the storage system. Two methods can be considered for introducing a new storage device to the storage system. One method is to replace the old storage device with a new storage device. Another method is to make the old storage device and new storage device coexist.
Nevertheless, when making a full transition from the old storage device to a new storage device, the old storage device cannot be utilized. Meanwhile, when making the old storage device and new storage device coexist, the configuration of the storage system will become complex, and the management and operation thereof will become extremely troublesome.
Thus, the present applicant has proposed technology of connecting a host and a first storage device and connecting the first storage device and a second storage device so that the first storage device will act over and process the access request from the host (Japanese Patent Laid-Open Publication No. 2004-005370). With this technology, the first storage device will also receive and process commands targeting the second storage device. If necessary, the first storage device issues a command to the second storage device, receives the processing result thereof, and transmits this to the host.
With the conventional technology described in the foregoing document, the performance of the storage system is improved by making the first storage device and second storage device coexist without wasting any memory resource. Nevertheless, even with this kind of reinforced storage system, the processing performance may deteriorate during the prolonged operation thereof.
For example, if the number of hosts connected to the first storage device increases, since numerous access requests will be issued from the respective hosts, the processing performance of the storage system will most likely deteriorate. Further, data to be managed will increase daily, and the method of use and frequency of use will differ diversely according to the nature of the respective data.
Thus, further reinforcement of the storage system is desired. In such a case, the first storage device may be replaced with a different high-performance storage device, or a separate first storage device may be added to the existing first storage device. Nevertheless, the addition or replacement of the first storage device cannot be conducted as with the addition of the first storage device described in the foregoing document. This is because the first storage device is serially connected to the second storage device and uses the memory resource of the second storage device, and the configuration of the storage system is already complicated. The first storage device cannot be simply added or replaced by only focusing attention on the first storage device.